It is frequently necessary to attach a generator, typically a three-phase generator, to another machine; to decrease the axial length, and to utilize existing bearings, it has been proposed to form the shaft of the existing machine with a conical projection, for example in the form of a stub shaft, with which a shaft element of the generator can be engaged. This shaft element of the generator then carries the rotor structure thereof. The air gap between the rotor structure of the generator and the stator thereof is critical. This is particularly so if the generator is of the slip-ringless, interdigited or claw pole-type construction, in which a stationary field is used, the armature winding is likewise stationary, and the rotor is in form of magnetically conductive elements, with interruptions, which rotates in the space between the stator field and the stator armature, thus relating in two air gaps, that is, between the field and the rotor and between the rotor and the armature. Accurate positioning of the stationary and the rotary elements is therefore of prime importance so that the air gaps will be uniform. This requires extreme accuracy in manufacture both of the generator as well as of the matching machine components, and additionally extreme accuracy in assembly--frequently difficult to obtain, particularly under field assembly conditions. This type of generator is particularly suited as an exciter generator for use with prime movers, such as turbines, engines of various types, or transmission units, to provide additional electrical power by external association of the generator with a shaft of the prime mover, gear, or the like, which may be termed, collectively, "rotary machine," and providing the motive power for the generator.